The total sulfur in gasoline after 2005 will be limited to less than 30 wppm, while the total sulfur in diesel after 2006 will be limited to a maximum of 15 wppm. Various refinery processes, such as hydrodesulfurization, are commercially used to produce refined hydrocarbon streams that meet these low sulfur requirements. Unfortunately, a substantial fraction of these refined streams are transported via a pipeline that is also used for transporting high sulfur content crude and other sulfur-containing petroleum streams. When low sulfur transportation fuels are transported through such a pipeline they often pick-up unacceptable levels of both elemental sulfur and organic sulfur, some of which are relatively high boiling materials. This sulfur contamination can occur not only from crude carry-over, but also from cross-contamination between different refined streams. For example, a jet fuel containing up to about 3,000 wppm sulfur can contaminate low sulfur gasoline and distillate product streams. When the refined low sulfur product stream reaches a distribution terminal at the end of the pipeline, it will often contain a level of sulfur compounds that is too high to meet governmental regulations, and thus the stream must undergo an additional step to remove sulfur moieties to an acceptable level. Although the exact mechanism for sulfur pick-up is unknown, it is believed that reactive sulfur molecules from crude or high sulfur-containing product streams adsorb on the pipeline walls during the crude or high sulfur product cycles. These sulfur molecules will then desorb into the ultra-low sulfur product streams during the ultra-low sulfur product cycles in the pipeline delivery sequences.
Various techniques have been reported for removing both elemental and organic sulfur from petroleum product streams, including conventional high severity hydrodesulfurization in the presence of a Group VIII/Group VI supported catalyst and hydrogen. Also, U.S. Pat. No. 4,149,966 discloses a method for removing elemental sulfur from refined hydrocarbon streams by adding an organo-mercaptan compound plus a copper compound capable of forming a soluble complex with the mercaptan and sulfur. The stream is then contacted with an adsorbent material to remove the resulting copper complex and substantially all elemental sulfur.
U.S. Pat. No. 4,011,882 discloses a method for reducing sulfur contamination of refined hydrocarbon streams transported in a pipeline for the transportation of sweet and sour hydrocarbon streams by washing the pipeline with a wash solution containing a mixture of light and heavy amines, a corrosion inhibitor, a surfactant and an alkanol containing from 1 to 6 carbon atoms.
U.S. Pat. No.5,618,408 teaches a method for reducing the amount of sulfur and other sulfur contaminants picked-up by refined hydrocarbon products, such as gasoline and distillate fuels, that are shipped in a pipeline used to transport heavier sour hydrocarbon product streams. The method involves controlling the level of dissolved oxygen in the refined hydrocarbon stream that is to be pipelined.
Further, U.S. Pat. No. 5,199,978 teaches the use of an inorganic caustic material, an alkyl alcohol, and an organo mercaptan, or sulfide compound, capable of reacting with elemental sulfur to form a fluid-insoluble polysulfide salt reaction product at ambient temperatures.
Adsorption is often a cost-effective process to remove relatively low levels of contaminants. Salem, A. B. et al., “Removal of Sulfur Compounds from Naphtha Solutions Using Solid Adsorbents”, Chemical Engineering and Technology, Jun. 20, 1997, report a 65% reduction in the sulfur level (500 to 175 wppm) for a 50/50 mixture of virgin and cracked naphthas using activated carbon at 80° C. and a 30% reduction using Zeolite 13X at 80° C. Also, U.S. Pat. No. 5,807,475 teaches that Ni or Mo exchanged Zeolite X and Y can be used to remove sulfur compounds from hydrocarbon streams. Typical adsorption processes have an adsorption cycle whereby the contaminant is adsorbed from the stream followed by a desorption cycle whereby the adsorbent is regenerated by removing at least a portion, preferably substantially all, of the contaminants therefrom. Also, conventional bulk nickel adsorbents have been used to remove trace amounts of sulfur from naphtha streams. Such conventional bulk nickel adsorbents are only typically suitable for removing low levels of light mercaptan sulfur and do not have enough sulfur capacity to remove high molecular weight organic sulfur from distillate streams.
While such methods have met with varying degrees of success, there still exists a need in the art for reducing both elemental and organic sulfur pick-up by hydrocarbon product streams when transported through a pipeline. For example, high molecular weight sulfur species can be removed from such transported streams using conventional high severity hydrodesulfurization, the operating cost can be substantial. Therefore, there is a need in the art for technology that is capable of removing relatively low levels of high molecular weight sulfur compounds from hydrocarbon streams and at relatively low operating costs.